Hybrid brake systems and methods

ABSTRACT

A braking system for an aircraft may comprise: a brake assembly including a brake stack; an electric braking subsystem having an electric brake actuator configured to operate the brake assembly; and a controller in operable communication with the electric braking subsystem, the controller configured to perform a wear depth measurement process, the wear depth measurement process comprising: determine a reference position of the electric brake actuator; command the electric brake actuator to extend toward the brake stack; receive a force measurement from a load cell in response to the electric brake actuator contacting the brake stack; determine a linear travel distance of the electric brake actuator based on an end position determined from the force measurement; and determine a wear depth based on calculating a difference between the linear travel distance and a prior linear travel distance of the electric brake actuator.

FIELD

The present disclosure relates to aircraft wheel and brake systems and,more particularly, to systems and methods for brake wear measurement inaircraft wheel and brake systems.

BACKGROUND

Aircraft typically utilize brake systems on wheels to slow or stop theaircraft during landings, taxiing and emergency situations, such as, forexample, a rejected take off (RTO). The brake systems generally employ aheat sink comprising a series of friction disks, disposed between apressure plate and an end plate, that may be forced into sliding contactwith one another during a brake application to slow or stop theaircraft. The friction disks wear over time.

A typical hydraulic brake system may include, without limitation, asource of pressurized hydraulic fluid, a hydraulic actuator for exertinga force across the heat sink (e.g., across the pressure plate, theseries of friction disks and the end plate), a valve for controlling apressure level provided to the hydraulic actuator and a brake controlunit for receiving inputs from a pilot and from various feedbackmechanisms and for producing responsive outputs to the valve. Uponactivation of the brake system (e.g., by depressing a brake pedal), apressurized fluid is applied to the hydraulic actuator, which maycomprise a piston configured to translate the pressure plate toward theend plate. A typical electric brake system includes variouselectromechanical counterparts to a hydraulic brake system, such as, forexample, an electromechanical brake actuator (EBA) in place of thehydraulic actuator and a source of electric power in place of the sourceof pressurized hydraulic fluid.

SUMMARY

A braking system for an aircraft is disclosed herein. The braking systemmay comprise: a brake assembly including a brake stack; an electricbraking subsystem having an electric brake actuator configured tooperate the brake assembly; and a controller in operable communicationwith the electric braking subsystem, the controller configured toperform a wear depth measurement process, the wear depth measurementprocess comprising: determining a reference position of the electricbrake actuator; commanding the electric brake actuator to extend towardthe brake stack; receiving a force measurement from a load cell inresponse to the electric brake actuator contacting the brake stack;determining a linear travel distance of the electric brake actuatorbased on an end position determined from the force measurement; anddetermining a wear depth based on calculating a difference between thelinear travel distance and a prior linear travel distance of theelectric brake actuator.

In various embodiments, the braking system further comprises a hydraulicbraking subsystem in operable communication with the controller, thehydraulic braking subsystem having a hydraulic brake actuator configuredto operate the brake assembly independently of the electric brakingsubsystem. The controller may be further configured to receive anindication that the braking system has been powered up prior todetermining a primary braking system for a prior flight cycle. Thecontroller may be further configured to: command the hydraulic brakingsubsystem to be the primary braking system for a current flight cycle inresponse to determining the electric braking subsystem was the primarybraking system for the prior flight cycle; and command the electricbraking subsystem to perform the wear depth measurement process. Thecontroller may be further configured to initiate the wear depthmeasurement process in response to the controller commanding a parkbrake release. The controller may be further configured to ensurebraking is not applied by the hydraulic braking subsystem prior toperforming the wear depth measurement process.

In various embodiments, the controller is further configured to performthe wear depth measurement process by commanding the electric brakeactuator to retract to a fully retracted position prior to commandingthe electric brake actuator to extend toward the brake stack. Thecontroller may be further configured to perform the wear depthmeasurement process by determining a reference position based onretracting the electric brake actuator to the fully retracted position.The linear travel distance may be based on the reference position andthe end position.

In various embodiments, the braking system may further comprise aplurality of the electric brake actuator disposed circumferentiallyabout a centerline of the brake stack, wherein the controller is furtherconfigured to measure an average wear of the brake stack based on thewear depth for each electric brake actuator in the plurality of theelectric brake actuator.

An article of manufacture is disclosed herein. The article ofmanufacture may include a tangible, non-transitory computer-readablestorage medium having instructions stored thereon that, in response toexecution by a processor, cause the processor to perform operationscomprising: commanding, via the processor, an electric brake actuator toretract to a fully retracted position to determine a reference position;commanding, via the processor, the electric brake actuator to extendfrom the reference position to an end position, the end positiondetermined based on receiving a force measurement from a load cell ofthe electric brake actuator; calculating, via the processor, a lineartravel distance of the electric brake actuator based on the referenceposition and the end position; and determining, via the processor, alocal wear depth of a friction disk based on calculating a differencebetween the linear travel distance and an initial linear traveldistance.

In various embodiments, the operations further comprise determining thelocal wear depth for a plurality of the electric brake actuator, theplurality of the electric brake actuator disposed circumferentiallyabout a centerline of a brake stack.

In various embodiments, the operations further comprise: determining,via the processor, a primary braking system for a prior flight cycle;and commanding, via the processor, a hydraulic braking subsystem to bethe primary braking system for a current flight cycle in response todetermining an electric braking subsystem was the primary braking systemfor the prior flight cycle. The operations may further comprise:activating, via the processor, the electric braking subsystem todetermine the local wear depth after commanding the hydraulic brakingsubsystem is the primary braking system for the current flight cycle;and determining, via the processor, braking is not being applied by thehydraulic braking subsystem prior to determining the local wear depth.The operations may further comprise commanding, via the processor,determining of the wear depth in response to a park brake releasecommand being received after determining a park brake is enabled.

An article of manufacture is disclosed herein. The article ofmanufacture may comprise a tangible, non-transitory computer-readablestorage medium having instructions stored thereon that, in response toexecution by a processor, cause the processor to perform operationscomprising: commanding, via the processor, activation of an electricbraking subsystem of a braking system in response to the braking systempowering up, the braking system comprising the electric brakingsubsystem and a hydraulic braking subsystem; commanding, via theprocessor, the electric brake actuator to extend from a referenceposition to an end position, the end position determined based onreceiving a force measurement from a load cell of the electric brakeactuator; and determining, via the processor, a local wear depth of afriction disk based on calculating a difference between a linear traveldistance from the reference position to the end position and an initiallinear travel distance.

In various embodiments, the operations further comprise determiningbraking is not being applied by the hydraulic braking subsystem prior tocommanding the electric brake actuator to extend.

In various embodiments, the operations further comprise determiningwhether the electric braking subsystem is a secondary braking system ora primary braking system after determining the local wear depth. Theoperations may further comprise deactivating the electric brakingsubsystem in response to determining the electric braking subsystem isthe secondary braking system.

In various embodiments, the operations further comprise determining thelocal wear depth for a plurality of the electric brake actuator, theplurality of the electric brake actuator disposed circumferentiallyabout a centerline of a brake stack.

The foregoing features and elements may be combined in any combination,without exclusivity, unless expressly indicated herein otherwise. Thesefeatures and elements as well as the operation of the disclosedembodiments will become more apparent in light of the followingdescription and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the following detailed description andclaims in connection with the following drawings. While the drawingsillustrate various embodiments employing the principles describedherein, the drawings do not limit the scope of the claims.

FIG. 1A illustrates an aircraft having multiple landing gear and brakes,in accordance with various embodiments;

FIG. 1B is a block diagram of a brake control unit, in accordance withvarious embodiments;

FIG. 1C is a schematic diagram of a brake assembly, in accordance withvarious embodiments;

FIGS. 2A and 2B are functional diagrams of a hybrid or redundant brakingsystem, in accordance with various embodiments;

FIG. 3 illustrates a process for operating the hybrid or redundantbraking system, in accordance with various embodiments;

FIG. 4 illustrates a process for operating the hybrid or redundantbraking system, in accordance with various embodiments;

FIG. 5 illustrates a process for determining a local wear depth of afriction disk for an electric braking system, in accordance with variousembodiments; and

FIG. 6 illustrates a process for determining an average wear depth of afriction disk for an electric braking system, in accordance with variousembodiments.

DETAILED DESCRIPTION

The following detailed description of various embodiments herein makesreference to the accompanying drawings, which show various embodimentsby way of illustration. While these various embodiments are described insufficient detail to enable those skilled in the art to practice thedisclosure, it should be understood that other embodiments may berealized and that changes may be made without departing from the scopeof the disclosure. Thus, the detailed description herein is presentedfor purposes of illustration only and not of limitation. Furthermore,any reference to singular includes plural embodiments, and any referenceto more than one component or step may include a singular embodiment orstep. Also, any reference to attached, fixed, connected, or the like mayinclude permanent, removable, temporary, partial, full or any otherpossible attachment option. Additionally, any reference to withoutcontact (or similar phrases) may also include reduced contact or minimalcontact. It should also be understood that unless specifically statedotherwise, references to “a,” “an” or “the” may include one or more thanone and that reference to an item in the singular may also include theitem in the plural. Further, all ranges may include upper and lowervalues and all ranges and ratio limits disclosed herein may be combined.

Methods for avoiding latent brake failure, as well as methods ofmitigating latent brake failure, are disclosed herein.

Referring now to FIG. 1A, an aircraft 100 includes multiple landing gearsystems, including a first landing gear 102 (or a port-side landinggear), a second landing gear 104 (or a nose landing gear) and a thirdlanding gear 106 (or a starboard-side landing gear). The first landinggear 102, the second landing gear 104 and the third landing gear 106each include one or more wheel assemblies. For example, the thirdlanding gear 106 includes an inner wheel assembly 108 and an outer wheelassembly 110. The first landing gear 102, the second landing gear 104and the third landing gear 106 support the aircraft 100 when theaircraft 100 is not flying, thereby enabling the aircraft 100 to takeoff, land and taxi without incurring damage. In various embodiments, oneor more of the first landing gear 102, the second landing gear 104 andthe third landing gear 106 is operationally retractable into theaircraft 100 while the aircraft 100 is in flight.

In various embodiments, the aircraft 100 further includes an avionicsunit 112, which includes one or more controllers (e.g., processors) andone or more tangible, non-transitory memories capable of implementingdigital or programmatic logic. In various embodiments, for example, theone or more controllers are one or more of a general purpose processor,digital signal processor (DSP), application specific integrated circuit(ASIC), field programmable gate array (FPGA) or other programmable logicdevice, discrete gate, transistor logic, or discrete hardware component,or any of various combinations thereof or the like. In variousembodiments, the avionics unit 112 controls operation of variouscomponents of the aircraft 100. For example, the avionics unit 112controls various parameters of flight, such as an air traffic managementsystems, auto-pilot systems, auto-thrust systems, crew alerting systems,electrical systems, electronic checklist systems, electronic flight bagsystems, engine systems flight control systems, environmental systems,hydraulics systems, lighting systems, pneumatics systems, trafficavoidance systems, trim systems, brake systems and the like.

In various embodiments, the aircraft 100 further includes brake controlunits (BCUs) 120 (e.g., hydraulic brake control unit 220 and electricbrake control unit 250 as described further herein). With briefreference now to FIG. 1B, the BCUs 120 include one or more controllers115 (e.g., processors) and one or more memories 116 (e.g., tangible,non-transitory memories) capable of implementing digital or programablelogic. In various embodiments, for example, the one or more controllers115 is one or more of a general purpose processor, DSP, ASIC, FPGA, orother programmable logic device, discrete gate, transistor logic, ordiscrete hardware component, or any of various combinations thereof orthe like, and the one or more memories 116 is configured to storeinstructions that are implemented by the one or more controllers 115 forperforming various functions, such as adjusting the hydraulic pressureor electric power provided to a brake actuator depending on the degreeof braking desired. In various embodiments, the BCUs 120 control thebraking of the aircraft 100. For example, the BCUs 120 control variousparameters of braking, such as manual brake control, automatic brakecontrol, antiskid braking, locked wheel protection, touchdownprotection, emergency/parking brake monitoring or gear retractionbraking. The BCUs 120 may further include hardware 117 capable ofperforming various logic using discrete power signals received fromvarious aircraft systems. Referring again to FIG. 1A, the aircraft 100further includes one or more brake assemblies coupled to each wheelassembly. For example, a brake assembly 118 is coupled to the outerwheel assembly 110 of the third landing gear 106 of the aircraft 100.During operation, the brake assembly 118 applies a braking force to theouter wheel assembly 110 upon receiving a brake command from the BCUs120. In various embodiments, the outer wheel assembly 110 of the thirdlanding gear 106 of the aircraft 100 (or of any of the other landinggear described above and herein) comprises any number of wheels or brakeassemblies.

Referring now to FIG. 1C, schematic details of the brake assembly 118illustrated in FIG. 1A are provided. In various embodiments, the brakeassembly 118 is mounted on an axle 130 for use with a wheel 132 disposedon and configured to rotate about the axle 130 via one or more bearingassemblies 134. A central axis 136 extends through the axle 130 anddefines a center of rotation of the wheel 132. A torque plate barrel 138(sometimes referred to as a torque tube or barrel or a torque plate) isaligned concentrically with the central axis 136, and the wheel 132 isrotatable relative to the torque plate barrel 138. The brake assembly118 includes an actuator ram assembly 140, a pressure plate 142 disposedadjacent the actuator ram assembly 140, an end plate 144 positioned adistal location from the actuator ram assembly 140, and a plurality ofrotor disks 146 interleaved with a plurality of stator disks 148positioned intermediate the pressure plate 142 and the end plate 144.The pressure plate 142, the plurality of rotor disks 146, the pluralityof stator disks 148 and the end plate 144 together form a brake heatsink or brake stack 150. The pressure plate 142, the end plate 144 andthe plurality of stator disks 148 are mounted to the torque plate barrel138 and remain rotationally stationary relative to the axle 130. Theplurality of rotor disks 146 is mounted to the wheel 132 and rotate withrespect to each of the pressure plate 142, the end plate 144 and theplurality of stator disks 148.

An actuating mechanism for the brake assembly 118 includes a pluralityof actuator ram assemblies, including the actuator ram assembly 140,circumferentially spaced around a piston housing 152 (only one actuatorram assembly is illustrated in FIG. 1C). Upon actuation, the pluralityof actuator ram assemblies affects a braking action by urging thepressure plate 142 and the plurality of stator disks 148 into frictionalengagement with the plurality of rotor disks 146 and against the endplate 144. Through compression of the plurality of rotor disks 146 andthe plurality of stator disks 148 between the pressure plate 142 and theend plate 144, the resulting frictional contact slows or stops orotherwise prevents rotation of the wheel 132. In various embodiments,the plurality of rotor disks 146 and the plurality of stator disks 148are fabricated from various materials, such as, for example, ceramicmatrix composite materials, that enable the brake disks to withstand anddissipate the heat generated during and following a braking action. Asdiscussed in further detail below, in various embodiments, the actuatorram assemblies comprise a combination of electrically operated actuatorrams (or electric brake actuators) and hydraulically operated actuatorrams (or hydraulic brake actuators).

Referring now to FIG. 2A, a braking system 200 (or a redundant brakingsystem or a hybrid braking system) is illustrated, in accordance withvarious embodiments. Generally, the braking system 200 may be separatedinto a hydraulic braking subsystem 202 and an electric braking subsystem204. Referring first to the hydraulic braking subsystem 202, the brakingsystem 200 includes a hydraulic brake control unit 220, which isprogrammed to control the various braking functions performed by thehydraulic braking subsystem 202. The hydraulic braking subsystem 202includes a hydraulic power source 222 configured to provide a hydraulicfluid to a primary brake control module 224 via a primary hydraulic line226. A primary pressure transducer 228 senses the pressure of thehydraulic fluid and provides a signal reflective of the pressure to thehydraulic brake control unit 220 via a data circuit 230. In variousembodiments, the hydraulic braking subsystem 202 includes a hydraulicfluid return 232 that is configured to return hydraulic fluid from theprimary brake control module 224 to the hydraulic power source 222 via areturn hydraulic line 234.

A secondary hydraulic line 236 fluidly couples the primary brake controlmodule 224 to a brake assembly 218, similar to the brake assembly 118described above with reference to FIG. 1A. More particularly, thesecondary hydraulic line 236 is fluidly coupled to a hydraulic brakeactuator 217 (or a plurality of hydraulic brake actuators) housed withinthe brake assembly 218. In various embodiments, a fuse 238 is fluidlycoupled to the secondary hydraulic line 236 downstream of the primarybrake control module 224. The fuse 238 acts as a shut-off valve orswitch in the event the secondary hydraulic line 236 experiences a lossof pressure - e.g., in the event of a leak in the secondary hydraulicline 236 or the brake assembly 218 - thereby preventing hydraulic fluidfrom continuing to flow to the secondary hydraulic line 236 and leakingout of the hydraulic system. A secondary pressure transducer 240 isfluidly coupled to the secondary hydraulic line 236 and electricallycoupled to the hydraulic brake control unit 220 via the data circuit230. In the event the secondary pressure transducer 240 senses a loss ofpressure within the secondary hydraulic line 236, the hydraulic brakecontrol unit 220 may, in redundant fashion, pass control of the brakingsystem 200 to the electric braking subsystem 204. As illustrated, thesecondary hydraulic line 236, the fuse 238, the secondary pressuretransducer 240 and the brake assembly 218 are replicated for each of aplurality of outer wheel assemblies 210 and for each of a plurality ofinner wheel assemblies 211 comprised within the braking system 200.Without loss of generality, in various embodiments, the hydraulicbraking subsystem 202 also includes wheel speed transducers and braketemperature sensors, such as, for example, an inboard wheel speedtransducer 242 and an outboard wheel speed transducer 243, and aninboard brake temperature sensor 244 and an outboard brake temperaturesensor 245.

Referring now to the electric braking subsystem 204, the braking system200 includes an electric brake control unit 250, which is programmed tocontrol the various braking functions performed by the electric brakingsubsystem 204. The electric braking subsystem 204 includes an electricpower source 252 configured to provide electric power to an electricbrake actuator controller 254, which, for example, may be an inboardelectric brake actuator controller or an outboard electric brakeactuator controller. The electric power is provided to the electricbrake actuator controller 254 via an electric power circuit 257. Theelectric brake actuator controller 254 is electrically coupled to anelectric brake actuator 219 (or a plurality of electric brake actuators)that is housed within the brake assembly 218. In various embodiments,the electric brake actuator controller 254 includes or is connected to acontrol circuitry 256 configured to monitor various aspects of a brakingoperation. The electric brake actuator 219 may include, for example, aload cell 259 electrically coupled to the control circuitry 256 andconfigured to monitor the load applied via the electric brake actuator219. In various embodiments, the electric brake control unit 250provides force commands to the electric brake controller 254, which inturn provides a current command to the electric brake actuator 219 toapply force, directing the electric brake actuator 219 to cause thebrake assembly 218 to mechanically operate, thereby driving the brakeassembly 218 to provide braking power. In various embodiments, the brakeactuator controller 254 monitors the load cell 259 (e.g., via thecontrol circuitry 256) to apply more or less current to achieve adesired force. In various embodiments, the electric brake actuatorcontroller 254 is coupled to the electric brake control unit 250 via acommunication link 258. The communication link 258 may comprise, forexample, a controller area network bus 260. Similar to the hydraulicbraking subsystem 202, and without loss of generality, the electricbraking subsystem 204 also includes wheel speed transducers, such as,for example, an inboard wheel speed transducer 262 and an outboard wheelspeed transducer 263, or brake temperature sensors.

In various embodiments the load cell 259 for each electric brakeactuator 219 in the electric braking subsystem 204 measures a forceapplied to the brake stack 150 from FIG. 1C at the electric brakeactuator 219 location. In various embodiments, each electric brakeactuator 219 may comprise a corresponding load cell 259.

Referring now to FIG. 2B, the brake assembly 218 is described withfurther detail. As illustrated, the brake assembly 218 includes apressure plate 215 configured to apply a compressive load against abrake stack or heat sink, which includes a plurality of brake rotors anda plurality of brake stators sandwiched between the pressure plate andan end plate. As described above, the brake assembly 218 includes thehydraulic brake actuator 217 (or a plurality of such hydraulic brakeactuators) and the electric brake actuator 219 (or a plurality of suchelectric brake actuators). In various embodiments, the brake assembly218 includes four electric brake actuators spaced at ninety degree (90°)intervals about the pressure plate 215 and four hydraulic brakeactuators spaced at ninety degree (90°) intervals about the pressureplate 215, with each electric brake actuator and each hydraulic brakeactuator spaced at forty-five degree (45°) intervals. Fewer or greaternumbers of actuators, both electric and hydraulic, are contemplatedwithin the scope of the disclosure.

Referring back to FIG. 2A, during operation, a pilot or a co-pilotdepresses a pilot brake pedal 270 or a co-pilot brake pedal 272, each ofwhich is connected to a hydraulic brake position sensor 274 and to anelectric brake position sensor 276. The hydraulic brake position sensor274 generates a signal reflective of the pedal position that istransmitted to the hydraulic brake control unit 220 via a hydraulicbrake sensor bus 278. The hydraulic brake control unit 220, if employed,then activates the hydraulic brake actuator 217 based on a currentsignal that is transmitted to the primary brake control module 224 via aprimary brake control bus 225. Similarly, the electric brake positionsensor 276 generates a signal reflective of the pedal position that istransmitted to the electric brake control unit 250 via an electric brakesensor bus 280. The electric brake control unit 250, if employed, thenactivates the electric brake actuator 219 based on a force request thatis transmitted to the electric brake actuator controller 254 via thecommunication link 258. In various embodiments, an avionics system 282is configured to employ one or both of the hydraulic braking subsystem202 and the electric braking subsystem 204 via signals transmitted overa respective data bus 283. In various embodiments, an autobrake selector284 is configured to employ one or both of the hydraulic brakingsubsystem 202 and the electric braking subsystem 204 via signalstransmitted over an autobrake data bus 285.

The braking system 200 may operate in a fully hydraulic mode, employingonly the hydraulic braking subsystem 202, or in a fully electric mode,employing only the electric braking subsystem 204. In addition, thedisclosure contemplates, in various embodiments, the hydraulic brakingsubsystem 202 being employed as the principal braking system, while theelectric braking subsystem 204 is employed as a backup braking system inthe event a failure occurs with the hydraulic braking subsystem 202. Thedisclosure also contemplates, in various embodiments, the electricbraking subsystem 204 being employed as a parking brake when theaircraft is at rest. In various embodiments, the hydraulic brake controlunit 220 and the electric brake control unit 250 are configured tocommunicate with one another via an intercommunication bus 286. Suchcommunication enables, for example, transfer of control from thehydraulic brake control unit 220 to the electric brake control unit 250following a failure of the hydraulic braking subsystem 202. For example,in the event the hydraulic brake control unit 220 detects a leak ofhydraulic fluid within the hydraulic braking subsystem 202, thehydraulic brake control unit 220 may communicate with the electric brakecontrol unit 250 and transfer control of the braking system 200 to theelectric brake control unit 250. Similarly, in the event the electricbrake control unit 250 detects a failure within the electric brakingsubsystem 204, the electric brake control unit 250 may communicate withthe hydraulic brake control unit 220 and transfer control of the brakingsystem 200 to the hydraulic brake control unit 220. In this regard, aprimary braking system and a secondary braking system may be determinedfor each flight cycle, as described further herein. Based on a failureto the primary braking system being detected, the BCUs 120 areconfigured to transfer control from the primary braking system to thesecondary braking system.

The above disclosure provides for a hybrid braking architecture. Invarious embodiments, the architecture employs hydraulic power for normalbraking and electric power for an alternate braking system or a parkingbrake system. The architecture provides a fully redundant braking systemfor normal pedal operated braking and for emergency braking. In variousembodiments, the piston housing (e.g., the piston housing 152 referredto in FIG. 1C) is modified to accept four hydraulic actuators and fourelectric actuators, spaced equally and alternating between one hydraulicactuator and one electric actuator; though any number of actuators iscontemplated by the disclosure. The equal spacing of forty-five degrees(45°) between alternating hydraulic and electric brake actuators allowsfor uniform force application on the brake stack when the hydraulicsystem is active or the electric system is active.

In various embodiments, the architecture is operated using pedals in thecockpit. This allows seamless activity and minimum pilot effort when,for example, the emergency system is engaged. The architecture istransparent for actuation (e.g., automated), although crew-alertingsystem (CAS) messages may be employed to inform the pilot that theemergency system (e.g., the electric braking subsystem) has becomeactive. The hydraulic and electric brake control units are in constantcommunication using, for example, controller area network (CAN)communication links, such that when the primary brake control unit(either the hydraulic or the electric brake control unit) detects a lossof braking or other fault, the alternate brake control unit (either thehydraulic or the electric brake control unit) may take over control andoperate the braking. In various embodiments, a switch may also beprovided in the cockpit to allow the pilot to manually switch from theone braking subsystem to the other - e.g., the hydraulic subsystem tothe electric sub system - depending on the failure and any other issuesor faults occurring with the power supplies or other aircraft systemdegradations.

Referring now to FIG. 3 , a process 300 for operating the braking system200 is described, in accordance with various embodiments. The process300 starts in response to the braking system 200 powering up (block302). Once an aircraft 100 is parked at a gate, and a parking brake isset, aircraft engines, and the BCUs 120 may be powered down. Once theaircraft 100 is loaded with passengers and all maintenance checks havebeen performed, a pilot turns back on the BCUs 120 and the aircraftengines. In response to powering up the braking system 200 via the BCUs120 (i.e., the hydraulic brake control unit 220 and the electric brakecontrol unit 250), the process 300 is initiated.

The process 300 further comprises determining which brake subsystem(e.g., hydraulic braking subsystem 202 or electric braking subsystem204) was active during a prior flight cycle (step 304). Stated anotherway, the BCUs 120 (i.e., the hydraulic brake control unit 220 and theelectric brake control unit 250), prior to powering down a previousflight cycle, store (e.g., in the memory 116) the braking subsystemutilized in the previous flight cycle. Thus, in response to powering up,the BCUs 120 determine if the previous active system was the hydraulicbraking subsystem 202 in step 304.

In response to determining the hydraulic braking subsystem 202 wasutilized for the previous flight cycle, the BCUs 120 (e.g., via electricbrake control unit 250) activate the electric braking subsystem 204 as aprimary brake system for a current flight cycle (step 306). Similarly,in response to determining the electric braking subsystem 204 wasutilized for the previous flight cycle, the BCUs 120 (e.g., via thehydraulic brake control unit 220) activate the hydraulic brakingsubsystem 202 for the current flight cycle (step 308). After selecting aprimary brake system for sole use during the current flight cycle instep 306 or step 308, the process 300 ends at step 310.

Thus, the process 300 keeps track of which system (e.g., hydraulicbraking subsystem 202 or electric braking subsystem 204) was utilizedfor the previous flight cycle and alternates to the other subsystem forthe following flight cycle. In this regard, the process 300 facilitatesexercise of both systems (e.g., hydraulic braking subsystem 202 orelectric braking subsystem 204) frequently to avoid latent brakefailures. The process 300 further allows use of the electric brakeactuator 219 half of the time relative to conventional system, thusdoubling the life of the electric braking subsystem 204.

Referring now to FIG. 4 , a process 400 for operating the braking system200 with the electric brake control unit 250 to perform a brake wear pinmeasurement is illustrated, in accordance with various embodiments.

The process 400 comprises activating the electric braking subsystem 204(step 402) in response to the brake system powerup (step 302 fromprocess 300). In this regard, the electric braking subsystem 204 may beactivated in response to the brake system powering up regardless ofwhether the electric braking subsystem 204 is a primary or secondarybraking system for the respective flight cycle (e.g., determined fromprocess 300).

The process 400 further comprises determining whether the park brake isenabled (step 404).

In response to the park brake not being enabled, process 400 may end atblock 414. In this regard, the process 400 is to be initiated inresponse to the park brake being released in step 406. Thus, if the parkbrake is already disabled, the process 400 ends as to ensure that theprocess 400 is performed at an appropriate time.

In response to the park brake be enabled, the process 400 furthercomprises determining if the park release has been commanded (step 406).If the park release command has not been initiated, the process 400reverts back to step 404. In response to the park brake being commandedto release, the process 400 further comprises determining whetherbraking is being applied by the hydraulic brake system (step 410). Inthis regard, if the hydraulic brake system is the primary brake system,as determined from the process 300, and currently in use, the process400 ends at block 414.

In various embodiments, if braking is not being applied by the hydraulicbrake system, a brake wear measurement is performed (e.g., in accordancewith process 500 shown in FIG. 5 and described further herein) (step408).

After the brake wear measurement is performed in step 408, the process400 further comprises determining whether the electric braking subsystem204 is the primary system or the secondary system for the respectiveflight cycle (e.g., as determined by process 300 described previouslyherein) (step 410). If the electric braking subsystem 204 is the primarybrake system, the electric braking subsystem 204 remains active and theprocess ends at block 414. If the electric braking subsystem 204 is thesecondary brake system, the process 400 further comprises deactivatingthe electric braking subsystem 204 prior to the flight cycle (step 412),in accordance with various embodiments.

Referring now to FIG. 5 , a process 500 for determining local wear isillustrated, in accordance with various embodiments. The process 500 maybe performed by the electric brake control unit 250, or the like. Invarious embodiments, the process 500 may be performed in the brakingsystem 200 (e.g., a hybrid and/or redundant braking system) or in anelectric brake system only. The present disclosure is not limited inthis regard.

The process 500 comprises commanding an electric brake actuator 219 toretract to a fully retracted state (step 502). A “fully retracted state”as defined herein refers to a point where the actuator cannot retractany further or can nearly not retract any further. In this regard,during normal operation, the electric brake actuator 219 may only bepartially retracted (i.e., enough retraction to ensure the electricbrake actuator 219 does not interfere with the hydraulic braking beingperformed by the hydraulic braking subsystem 202).

The process 500 further comprises determining a reference position basedon retracting the electric brake actuator 219 (step 504). In thisregard, retracting the electric brake actuator 219 to the fullyretracted state in step 502 may provide a consistent reference point forbrake wear measurements via process 500.

The process 500 further comprises commanding the electric brake actuator219 to extend from the fully retracted state (step 506) and determine anend position based on receiving a force measurement from the load cell259 of the electric brake actuator 219 (step 508). In this regard, theforce measurement from the load cell 259 of the electric brake actuator219 may be approximately zero until the electric brake actuator 219contacts the brake stack 150. Upon contacting the brake stack 150, theforce measurement from the load cell 259 may start to increase fromzero. In this regard, the end position (e.g., for brake wear calculationpurposes) may be determined in response to the force measurementincreasing from zero in step 508.

The process 500 further comprises calculating a linear travel distanceof the electric brake actuator 219 from the reference position to theend position (step 510). In various embodiments, linear travel distanceis directly proportional to a number of rotations of a motor controllingthe electric brake actuator 219. For example, in various embodiments,each rotational turn of the motor corresponds to 0.001 inches (0.00254cm) or 0.0001 inches (0.000254 cm), or the like. In this regard, anumber of turns from the reference position to the end positioncorrelates directly to a linear distance traveled by the electric brakeactuator 219.

In various embodiments, the process 500 further comprises calculating alocal wear depth based on calculating a difference between the lineartravel distance from step 510 and a prior flight linear travel distance(step 512). In this regard, process 500 may be performed prior to eachand every flight cycle and stored in a database (e.g., memory 116 fromFIG. 1B). Thus, local wear may be calculated between flights (e.g.,current flight vs. immediately prior flight), calculated from a firstflight with the braking system 200 (e.g., current flight vs. firstflight), or calculated from a designed initial linear length (i.e., areference linear travel distance). The present disclosure is not limitedin this regard. In various embodiments, comparison to a first flightwith the braking system 200 may be desirable to provide a common pointof reference and determine a total wear for the brake assembly 218.

In various embodiments, the process 500 provides a local wear depth forthe end plate 144. In this regard, with reference now to FIG. 6 , whichshows a process 600 for determining an average wear depth of a frictiondisk in a brake assembly, the process 500 may be repeated for eachelectric brake actuator 219 of a brake assembly 218 from FIG. 2B (step602). The process 600 further comprises calculating an average weardepth for a friction disk (e.g., the end plate 144) based on a localwear depth calculated for each electric brake actuator 219 in the brakeassembly 218. In various embodiments, by averaging the local wear depthsfrom process 500, a more accurate picture of wear over a frictionsurface of the friction disk (e.g., end plate 144) may be determined.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosure. The scope of the disclosure is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to “at least one of A, B, or C” is usedin the claims, it is intended that the phrase be interpreted to meanthat A alone may be present in an embodiment, B alone may be present inan embodiment, C alone may be present in an embodiment, or that anycombination of the elements A, B and C may be present in a singleembodiment; for example, A and B, A and C, B and C, or A and B and C.Different cross-hatching is used throughout the figures to denotedifferent parts but not necessarily to denote the same or differentmaterials.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment,” “an embodiment,”“various embodiments,” etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Numbers, percentages, or other values stated herein are intended toinclude that value, and also other values that are about orapproximately equal to the stated value, as would be appreciated by oneof ordinary skill in the art encompassed by various embodiments of thepresent disclosure. A stated value should therefore be interpretedbroadly enough to encompass values that are at least close enough to thestated value to perform a desired function or achieve a desired result.The stated values include at least the variation to be expected in asuitable industrial process, and may include values that are within 10%,within 5%, within 1%, within 0.1%, or within 0.01% of a stated value.Additionally, the terms “substantially,” “about” or “approximately” asused herein represent an amount close to the stated amount that stillperforms a desired function or achieves a desired result. For example,the term “substantially,” “about” or “approximately” may refer to anamount that is within 10% of, within 5% of, within 1% of, within 0.1%of, and within 0.01% of a stated amount or value.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112(f) unless the element is expressly recitedusing the phrase “means for.” As used herein, the terms “comprises,”“comprising,” or any other variation thereof, are intended to cover anon-exclusive inclusion, such that a process, method, article, orapparatus that comprises a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus.

Finally, it should be understood that any of the above describedconcepts can be used alone or in combination with any or all of theother above described concepts. Although various embodiments have beendisclosed and described, one of ordinary skill in this art wouldrecognize that certain modifications would come within the scope of thisdisclosure. Accordingly, the description is not intended to beexhaustive or to limit the principles described or illustrated herein toany precise form. Many modifications and variations are possible inlight of the above teaching.

What is claimed is:
 1. A braking system for an aircraft, comprising: abrake assembly including a brake stack; an electric braking subsystemhaving an electric brake actuator configured to operate the brakeassembly; and a controller in operable communication with the electricbraking subsystem, the controller configured to perform a wear depthmeasurement process, the wear depth measurement process comprising:determining a reference position of the electric brake actuator;commanding the electric brake actuator to extend toward the brake stack;receiving a force measurement from a load cell in response to theelectric brake actuator contacting the brake stack; determining a lineartravel distance of the electric brake actuator based on the referenceposition and an end position determined from the force measurement; anddetermining a wear depth based on calculating a difference between thelinear travel distance and a prior linear travel distance of theelectric brake actuator.
 2. The braking system of claim 1, furthercomprising a hydraulic braking subsystem in operable communication withthe controller, the hydraulic braking subsystem having a hydraulic brakeactuator configured to operate the brake assembly independently of theelectric braking subsystem.
 3. The braking system of claim 2, whereinthe controller is further configured to receive an indication that thebraking system has been powered up prior to determining a primarybraking system for a prior flight cycle.
 4. The braking system of claim3, wherein the controller is further configured to: command thehydraulic braking subsystem to be the primary braking system for acurrent flight cycle in response to determining the electric brakingsubsystem was the primary braking system for the prior flight cycle; andcommand the electric braking subsystem to perform the wear depthmeasurement process.
 5. The braking system of claim 4, wherein thecontroller is further configured to initiate the wear depth measurementprocess in response to the controller commanding a park brake release.6. The braking system of claim 4, wherein the controller is furtherconfigured to ensure braking is not applied by the hydraulic brakingsubsystem prior to performing the wear depth measurement process.
 7. Thebraking system of claim 1, wherein the controller is further configuredto perform the wear depth measurement process by commanding the electricbrake actuator to retract to a fully retracted position prior tocommanding the electric brake actuator to extend toward the brake stack.8. The braking system of claim 7, wherein the controller is furtherconfigured to perform the wear depth measurement process by determiningthe reference position based on retracting the electric brake actuatorto the fully retracted position.
 9. The braking system of claim 8,wherein the linear travel distance is based on the reference positionand the end position.
 10. The braking system of claim 1, furthercomprising a plurality of the electric brake actuator disposedcircumferentially about a centerline of the brake stack, wherein thecontroller is further configured to measure an average wear of the brakestack based on the wear depth for each electric brake actuator in theplurality of the electric brake actuator.
 11. An article of manufactureincluding a tangible, non-transitory computer-readable storage mediumhaving instructions stored thereon that, in response to execution by aprocessor, cause the processor to perform operations comprising:commanding, via the processor, an electric brake actuator to retract toa fully retracted position to determine a reference position;commanding, via the processor, the electric brake actuator to extendfrom the reference position to an end position, the end positiondetermined based on receiving a force measurement from a load cell ofthe electric brake actuator; calculating, via the processor, a lineartravel distance of the electric brake actuator based on the referenceposition and the end position; and determining, via the processor, alocal wear depth of a friction disk based on calculating a differencebetween the linear travel distance and one of a reference linear traveldistance.
 12. The article of manufacture of claim 11, wherein theoperations further comprise determining the local wear depth for aplurality of the electric brake actuator, the plurality of the electricbrake actuator disposed circumferentially about a centerline of a brakestack.
 13. The article of manufacture of claim 11, wherein theoperations further comprise: determining, via the processor, a primarybraking system for a prior flight cycle; and commanding, via theprocessor, a hydraulic braking subsystem to be the primary brakingsystem for a current flight cycle in response to determining an electricbraking subsystem was the primary braking system for the prior flightcycle.
 14. The article of manufacture of claim 13 wherein the operationsfurther comprise: activating, via the processor, the electric brakingsubsystem to determine the local wear depth after commanding thehydraulic braking subsystem is the primary braking system for thecurrent flight cycle; and determining, via the processor, braking is notbeing applied by the hydraulic braking subsystem prior to determiningthe local wear depth.
 15. The article of manufacture of claim 14,wherein the operations further comprise commanding, via the processor,determining of the wear depth in response to a park brake releasecommand being received after determining a park brake is enabled.
 16. Anarticle of manufacture including a tangible, non-transitorycomputer-readable storage medium having instructions stored thereonthat, in response to execution by a processor, cause the processor toperform operations comprising: commanding, via the processor, activationof an electric braking subsystem of a braking system in response to thebraking system powering up, the braking system comprising the electricbraking subsystem and a hydraulic braking subsystem; commanding, via theprocessor, an electric brake actuator to extend from a referenceposition to an end position, the end position determined based onreceiving a force measurement from a load cell of the electric brakeactuator; and determining, via the processor, a local wear depth of afriction disk based on calculating a difference between a linear traveldistance from the reference position to the end position and a referencelinear travel distance.
 17. The article of manufacture of claim 16,wherein the operations further comprise: determining braking is notbeing applied by the hydraulic braking subsystem prior to commanding theelectric brake actuator to extend.
 18. The article of manufacture ofclaim 16, wherein the operations further comprise determining whetherthe electric braking subsystem is a secondary braking system or aprimary braking system after determining the local wear depth.
 19. Thearticle of manufacture of claim 18, wherein the operations furthercomprise deactivating the electric braking subsystem in response todetermining the electric braking subsystem is the secondary brakingsystem.
 20. The article of manufacture of claim 16, wherein theoperations further comprise determining the local wear depth for aplurality of the electric brake actuator, the plurality of the electricbrake actuator disposed circumferentially about a centerline of a brakestack.